The present invention relates to a headlamp for a motor vehicle wherein near-ultraviolet rays emitted from a discharge bulb used as a light source are employed to illuminate an area beyond the area lit by the conventional low headlamp beam.
FIG. 4 is a sectional view of a headlamp of the foregoing type. In the drawing, reference numeral 1 designates a lamp body, and reference numeral 2 designates a front lens. A parabolic reflector 3 is arranged in the lamp body 1, a discharge-type bulb 4, e.g., a discharge lamp or the like which irradiates a wide spectrum of ultraviolet rays, is disposed at the focus position of the reflector 3, and a bandpass filter 5 which absorbs visible light components but permits ultraviolet rays to pass is disposed at a predetermined position in front of the reflector 3. With this construction, since the light beam emitted from the headlamp has a strong ultraviolet component since the visible components are absorptively removed by the bandpass filter 5, when the beam strikes an indicator such as certain sign boards or a pedestrian's safety jacket or the like containing, for instance, a fluorophosphor-based substance, fluorescent light is generated therefrom, resulting in the sign, jacket, etc., being easily seen by the driver. When used in combination with a low-beam headlamp emitting visible light, such a sign, jacket, etc., located relatively far ahead of the vehicle can be seen without blinding the driver of an oncoming vehicle, such as would occur if the high-beam headlamp were used.
However, with the conventional headlamp constructed in the above-described manner, since visible light components are absorptively removed by the bandpass filter, the overall brightness is generally insufficient. Thus, there arises a problem that the conventional headlamp must be used in combination with another type of headlamp, e.g., a low-beam headlamp.